The assembly of microparticles into large-scale structures is a proven and efficient method for the fabrication of structured materials with relevance to a wide variety of devices for photonic, electronic, magnetic, and sensor applications. See M. Boncheva and G. M. Whitesides, MRS Bull. 30, 736 (2005); and G. M. Whitesides and B. Grzybowski, Science 295, 2418 (2002). In comparison with techniques that rely on the spontaneous self-organization of particles into desired patterns, the use of optical, acoustic, electric, and magnetic fields to trap and transport the particles offers a significantly higher level of precision for the control of the particle positions. See B. A. Grzybowski et al., Nat. Mater. 2, 241 (2003); P. J. Burke, Nanodielectrophoresis: Electronic Nanotweezers, Encyclopedia of Nanoscience and Nanotechnology Vol. 6, edited by H. S. Nalwa (American Scientific, Stevenson Ranch, Calif., 2004), pp. 623-641; M. Riegelman et al., ASME J. Fluids Eng. 128, 6 (2006); J. P. Hoogenboom et al., Appl. Phys. Lett. 80, 4828 (2002); W. D. Ristenpart et al., Phys. Rev. Lett. 90, 128303 (2003); and B. B. Yellen et al., Proc. Natl. Acad. Sci. U.S.A. 102, 8860 (2005). A characteristic feature of these field-based methods is that all of them utilize a force exerted by a strong field gradient on an individual particle to trap it in regions of minimum or maximum field strength. When such a trap is displaced, the gradient force thereby generated causes an entrapped particle to follow the trap motion. Although precise, these techniques are slow since they deliver particles to a work area one at a time. To speed up the process, techniques recently reported in the literature involve the parallel transportation of particles by creating and simultaneously translating multiple field traps which, however, still contain a single particle. See P. Y. Chiou et al., Nature (London) 436, 370 (2005); T. P. Hunt et al., Appl. Phys. Lett. 85, 6421 (2004); I. R. Perch-Nielsen et al., Opt. Express 13, 2852 (2005); and D. G. Grier, Nature (London) 424, 810 (2003).
Therefore, a need remains for a device and method to collectively assemble and transport microparticles to enable formation of large-scale structures.